JP5331419B2 - Positive electrode material for lithium ion secondary battery and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode material for a lithium ion secondary battery capable of efficiently attaching a conducting active material to the surfaces of lithium iron phosphate particles and to provide the manufacturing method of the positive electrode material. <P>SOLUTION: Precursor glass for a positive electrode material for the lithium ion secondary battery contains a composition of 25-50% Li<SB>2</SB>O, 5-40% Fe<SB>2</SB>O<SB>3</SB>, and 20-50% Fe<SB>2</SB>O<SB>5</SB>in mol% expressed in terms of oxides. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

The present invention relates to a positive electrode material for lithium ion secondary batteries used in portable electronic devices and electric vehicles, and a method for producing the same. More specifically, the present invention relates to a lithium iron phosphate positive electrode material that is inexpensive and highly safe, replacing the conventional lithium cobalt oxide (LiCoO ₂ ), and a method for producing the same.

Lithium ion secondary batteries have established themselves as high-capacity and light-weight power supplies essential for portable electronic terminals and electric vehicles. In the past, inorganic metal oxides such as lithium cobaltate and lithium manganate (LiMnO ₂ ) have been used as the positive electrode material of the lithium ion secondary battery. With the recent increase in power consumption due to higher performance of electronic devices, further increase in capacity of lithium ion secondary batteries is required. In addition, from the viewpoint of environmental conservation problems and energy problems, there is a demand for switching from materials with a large environmental load such as Co and Mn to more environmentally conscious materials. Further, in recent years, the problem of depletion of cobalt resources has attracted attention, and from such a viewpoint, conversion to an inexpensive positive electrode material replacing LiCoO ₂ is desired.

In recent years, manganese spinel-type, NASICON-type Li ₃ Fe ₂ (PO ₄ ) ₃ and olivine-type LiFePO ₄ crystals have attracted attention among lithium compounds containing iron because they are advantageous in terms of cost and resources. Various researches and developments are underway (see, for example, Patent Document 1). Among them, olivine-type LiFePO ₄ is superior in temperature stability to LiCoO ₂ and is expected to operate safely at high temperatures. Further, because of the structure having phosphoric acid as a skeleton, it has a feature of excellent resistance to structural deterioration due to charge / discharge reaction.

It is known that the iron sites of manganese spinel type, NASICON type Li ₃ Fe ₂ (PO ₄ ) ₃ and olivine type LiFePO ₄ crystals can be replaced with various transition metal ions. For example, Li ₃ Mn ₂ (PO ₄ ) ₃ , LiMnPO _4, etc., in which iron is completely replaced with manganese, partially substituted Li ₃ (Mn _x Fe _1-x ) ₂ (PO ₄ ) ₃ , LiMn _x Fe _{1 -x PO 4 (0 <x <} 1) , etc. also has a function as a cathode material.

The characteristics required for the positive electrode material of the lithium ion secondary battery include high ionic conductivity and high electronic conductivity, but it has been reported that the electronic conductivity of the lithium iron phosphate positive electrode material is lower than that of LiCoO _2. ing.

JP-A-9-134725

  It is known that when a conductive active material such as carbon is mixed with a lithium iron phosphate positive electrode material, the electron conductivity is increased. However, when the conductive active material is mixed simultaneously with the firing of the lithium iron phosphate, the conductive active material cannot be efficiently activated on the surface of the lithium iron phosphate particles due to the influence of the gas generated from the raw material, and the electronic conductivity decreases.

  This invention is made | formed in view of such a condition, and provides the lithium ion secondary battery positive electrode material which can provide a conductive active material efficiently to the lithium iron phosphate particle surface, and its manufacturing method. For the purpose.

As a result of studying to solve the above problems, a precursor glass (crystalline glass) for depositing lithium iron phosphate crystals (LiFePO ₄ crystals and Li ₃ Fe ₂ (PO ₄ ) ₃ crystals) is used as a positive electrode material for lithium ion secondary batteries. By using as a raw material, it is possible to efficiently combine the fired crystallized glass powder with a conductive active material that improves electron conductivity without releasing gas when the powder is fired, and highly conductive lithium ions The present inventors have found that a secondary battery positive electrode material can be obtained and propose it as the present invention.

That is, the present invention is, in mol% in terms of _{oxide, Li 2 O 20~50%, Fe} 2 O 3 5~40%, lapis lazuli lithium-ion two to containing the composition of _P 2 O 5 20 to 50% The present invention relates to a positive electrode material for a lithium ion secondary battery, comprising crystallized glass powder for a secondary battery positive electrode material and a conductive active material .

  In order to obtain excellent conductivity as a positive electrode material for a battery, both ion conductivity and electron conductivity are required to be good. Therefore, in the present invention, by firing the precursor glass powder, a crystallized glass powder having a small crystallite size on which lithium iron phosphate crystals having a homogeneous composition are precipitated can be produced, and the ion conductivity is reduced. It was possible to obtain a positive electrode material for a lithium ion secondary battery excellent in the above. In addition, the precursor glass is mixed with a conductive active material and fired, or the precursor glass powder is fired and the conductive active material is mixed to efficiently activate the conductive active material on the surface of the crystallized glass powder particles. Thus, it is possible to obtain a lithium ion secondary battery positive electrode material that compensates for insufficient electron conductivity and is excellent in conductivity.

Second, the lithium ion secondary battery positive electrode material of the present invention, the crystallized glass powder further contains a MnO _2, the content of MnO ₂ of the crystallized glass powder is moles of oxide equivalent It is characterized by being 55% or less in% display .

Thirdly , in the lithium ion secondary battery positive electrode material of the present invention, the crystallized glass powder is further expressed in terms of mol% in terms of the following oxide, Nb ₂ O ₅ + V ₂ O ₅ + SiO ₂ + B ₂ O ₃ + GeO. It is characterized by containing a composition of ₂ + Al ₂ O ₃ + Ga ₂ O ₃ + Sb ₂ O ₃ + Bi ₂ O ₃ 0.1 to 25%.

Fourth, the lithium ion secondary battery positive electrode material of the present invention, the crystallized glass powder, LiFePO ₄ crystal or _{Li 3 Fe 2 (PO 4)} 3 crystal, or those made by precipitating solid solution thereof It is characterized by that.

Fifth, the lithium ion secondary battery positive electrode material of the present invention, the crystallized glass _{powder, LiMn X Fe 1-x PO} 4 crystal or _{Li 3 (Mn x Fe 1-} x) 2 (PO 4) 3 crystalline characterized in that (0 <x <1) is made to precipitate.

Sixth , the lithium ion secondary battery positive electrode material of the present invention is characterized in that the content of the conductive active material is 0.1 to 50 parts by mass with respect to 100 parts by mass of the crystallized glass powder.

Seventh , the positive electrode material of the lithium ion secondary battery of the present invention is characterized in that the conductive active material is a carbon-based conductive active material.

Eighth , the lithium ion secondary battery positive electrode material of the present invention is characterized in that the carbon-based conductive active material is graphite, acetylene black or amorphous carbon.

Ninth , the present invention includes (1) a composition expressed by mol% in terms of the following oxides, and Li ₂ O 20-50%, Fe ₂ O ₃ 5-40%, P ₂ O ₅ 20-50%. (2) a step of melting the batch to obtain a molten glass , ( 3) a step of rapidly cooling the molten glass to obtain a precursor glass, and (4) pulverizing the obtained precursor glass. A step of obtaining a precursor glass powder, and (5) a step of baking the precursor glass powder at a glass transition temperature to 1000 ° C. to obtain a crystallized glass powder. In step (5), an organic compound is added to the glass powder. In addition, the present invention relates to a method for producing a positive electrode material for a lithium ion secondary battery, wherein a carbon-based conductive active material derived from an organic compound is activated in crystallized glass powder by firing in an inert or reducing atmosphere .

Tenth , in the method for producing a positive electrode material for a lithium ion secondary battery of the present invention, when preparing the batch in step (1), the batch further contains MnO ₂ , and The batch is prepared so that the content of MnO ₂ is 55% or less in terms of mol% in terms of oxide .

Eleventh , the method for producing a positive electrode material for a lithium ion secondary battery according to the present invention further includes, in the step (1), Nb ₂ O ₅ + V ₂ O ₅ + SiO ₂ + B _{2 in} terms of the following oxide equivalent mol%. It is characterized in that the batch is formulated to contain 0.1-25% composition of O ₃ + GeO ₂ + Al ₂ O ₃ + Ga ₂ O ₃ + Sb ₂ O ₃ + Bi ₂ O ₃ .

Twelfth , the method for producing a positive electrode material for a lithium ion secondary battery according to the present invention is characterized in that the carbon-based conductive active material is amorphous carbon.

Thirteenthly , the method for producing a positive electrode material for a lithium ion secondary battery according to the present invention is characterized in that the organic compound is glucose, carboxylic acid or an organic binder.

Fourteenth, method for producing a lithium ion secondary battery positive electrode material of the present invention, the organic compound is characterized in that an acrylic resin.

The precursor glass for a lithium ion secondary battery positive electrode material according to the present invention is expressed in terms of mol% in terms of the following oxides, and Li ₂ O 20 to 50%, Fe ₂ O ₃ 5 to 40%, P ₂ O ₅ 20 to 50. % Composition.
The reason for limiting the composition as described above will be described below.

Li ₂ O is a main component of lithium iron phosphate. The content of Li ₂ O is 20 to 50%, preferably 25 to 45%. When the content of Li ₂ O is less than 20% or more than 50%, it is difficult to precipitate lithium iron phosphate crystals even when the obtained glass is fired.

Fe ₂ O _{3 is} also a main component of lithium iron phosphate. The content of Fe ₂ O ₃ is 5 to 40%, preferably 10 to 40%, more preferably 15 to 35%. When the content of Fe ₂ O ₃ is less than 5% or more than 40%, it becomes difficult to precipitate lithium iron phosphate crystals even when the obtained glass is fired. Incidentally, it may be used FeO as the raw material, the amount that case the terms of Fe ₂ O ₃ may satisfy the above range.

P ₂ O _{5 is} also a main component of lithium iron phosphate. The content of P ₂ O ₅ is 20 to 50%, preferably 25 to 45%. When the content of P ₂ O ₅ is less than 20% or more than 50%, it becomes difficult to precipitate lithium iron phosphate crystals even when the obtained glass is fired.

The precursor glass for a lithium ion secondary battery positive electrode material of the present invention may further contain MnO ₂ as a composition. MnO ₂ is partially substituted with Fe ₂ O ₃ to form a solid solution of LiMn _x Fe _1-x PO ₄ crystal or Li ₃ (Mn _x Fe _1-x ) ₂ (PO ₄ ) ₃ crystal (0 <x <1). Can be deposited. The content of MnO ₂ is 0 to 55%, preferably 15 to 50%, more preferably 20 to 40%. When the content of MnO ₂ exceeds 55%, vitrification becomes difficult.

Incidentally, on the relationship between MnO ₂ is replaced with _Fe 2 _{O 3,} it is preferred to limit the total amount of both components. Specifically, the total amount of Fe ₂ O ₃ and MnO ₂ is preferably 55% or less, more preferably 40% or less, and even more preferably 35% or less.

In the precursor glass for a lithium ion secondary battery positive electrode material of the present invention, the composition further includes Nb ₂ O ₅ + V ₂ O ₅ + SiO ₂ + B ₂ O ₃ + GeO ₂ + Al ₂ O ₃ + Ga ₂ O ₃ + Sb ₂ O ₃ + Bi. preferably contains ₂ O _{3 0.1~25%.}

Nb ₂ O ₅ , V ₂ O ₅ , SiO ₂ , B ₂ O ₃ , GeO ₂ , Al ₂ O ₃ , Ga ₂ O ₃ , Sb ₂ O ₃ and Bi ₂ O ₃ are components that improve glass forming ability. . If the total content of the oxides is less than 0.1%, vitrification becomes difficult. On the other hand, if the total content of the oxides is more than 25%, the electrical conductivity of the crystallized glass powder obtained by firing may be lowered.

The crystallized glass for a lithium ion secondary battery positive electrode material of the present invention is expressed in terms of mol% in terms of the following oxides, and Li ₂ O 20-50%, Fe ₂ O ₃ 5-40%, P ₂ O ₅ 20-50. % Composition. Further, Nb ₂ O ₅ + V ₂ O ₅ + SiO ₂ + B ₂ O ₃ + GeO ₂ + Al ₂ O ₃ + Ga ₂ O ₃ + Sb ₂ O ₃ + Bi ₂ O ₃ It is preferable to contain 0.1 to 25%. The reason for limiting the composition in this way is the same as described above.

The positive electrode material for a lithium ion secondary battery of the present invention is formed by depositing a LiFePO ₄ crystal or a Li ₃ Fe ₂ (PO ₄ ) ₃ crystal, or a solid solution crystal in which iron is replaced with another transition metal element such as manganese. Is preferred.

Conventional production methods of olivine-type LiFePO ₄ and NASICON-type Li ₃ Fe ₂ (PO ₄ ) ₃ crystals that have been attracting attention as positive electrode materials for lithium ion secondary batteries include conventional solid-phase reactions, hydrothermal synthesis, and microwaves. Although heating methods are known, these methods have problems in terms of productivity and particle size control. Therefore, since it is simpler, better in productivity and easy to vitrify, and a homogeneous and dense cathode material can be obtained, crystallization is performed after obtaining a precursor glass using a melt quench method as a production method. It is preferable to make it.

In addition, since the valence of iron in the olivine-type LiFePO ₄ is +2, it is likely to be oxidized to +3 due to redox equilibrium when melted for a long time in the atmosphere. Therefore, in order to control the valence state, a +2 valent reagent such as iron oxalate is added to the raw material for producing the precursor glass, or a reduction containing carbon such as glucose during the melting of the precursor glass. It is preferable to add the agent in the range of 0.01 to 50 parts by mass with respect to 100 parts by mass of the glass raw material. It is also preferable to melt in a reaction vessel excellent in airtightness filled with a reducing gas. Furthermore, once the precursor glass powder is prepared and heat-treated near the glass transition temperature in a reducing atmosphere of hydrogen, ammonia, carbon monoxide, etc., heat treatment is performed near the crystallization temperature after controlling the valence state. This is also effective in producing a crystallized glass powder composed of a single LiFePO ₄ . In addition, the organic binder added to mold the glass powder exhibits a reducing action by firing, so that the valence of iron in the glass changes to +2 before crystallization, so that it contains a high amount of LiFePO ₄ Can be obtained at a rate.

On the other hand, since the valence of iron in the NASICON-type Li ₃ Fe ₂ (PO ₄ ) ₃ crystal is +3, the raw material may be a raw material having a valence of +3 such as Fe ₂ O ₃ or a precursor. It is preferable to add an oxidizing agent such as peroxide, As ₂ O ₃ , Sb ₂ O ₃ during melting of the glass, or to melt in an oxygen stream. It is also effective to heat the precursor glass powder once produced in air or in an oxidizing gas in the vicinity of the glass transition temperature.

  The smaller the particle size of the crystallized glass powder, the larger the surface area of the positive electrode material as a whole, which is preferable because it facilitates the exchange of ions and electrons. Specifically, the average particle size of the crystallized glass powder is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. Although it does not specifically limit about a minimum, It is 0.05 micrometer or more actually.

The smaller the crystallite size of the LiFePO ₄ crystal or Li ₃ Fe ₂ (PO ₄ ) ₃ crystal in the crystallized glass powder, the smaller the particle size of the crystallized glass powder, and the better the electrical conductivity. it can. Specifically, the crystallite size is preferably 100 nm or less, and more preferably 80 nm or less. The lower limit is not particularly limited, but is actually 1 nm or more, and further 10 nm or more. The crystallite size is determined according to Scherrer's formula from the analysis result of powder X-ray diffraction relating to the crystallized glass powder.

The crystal content of LiFePO ₄ or Li ₃ Fe ₂ (PO ₄ ) _{3 in} the crystallized glass powder is preferably 20% by mass or more, more preferably 50% by mass or more, and 70% by mass or more. Further preferred. If the amount of crystals is less than 20% by mass, the conductivity tends to be insufficient. In addition, although it does not specifically limit about an upper limit, In reality, it is 99 mass% or less, Furthermore, it is 95 mass% or less.

  The desired crystallized glass powder can be produced by heat-treating the precursor glass powder obtained by pulverizing the precursor glass in an electric furnace capable of controlling the temperature and atmosphere. The temperature history of the heat treatment is not particularly limited because it varies depending on the composition of the precursor glass and the desired crystallite particle size, but it is appropriate to carry out the heat treatment at least at the glass transition temperature or even above the crystallization temperature. is there. The upper limit is 1000 ° C, and further 950 ° C. If the heat treatment temperature is lower than the glass transition temperature, there is a possibility that a sufficient conductivity improvement effect cannot be obtained. On the other hand, if the heat treatment temperature exceeds 1000 ° C., the crystals may melt. The specific temperature range for the heat treatment is preferably 500 to 1000 ° C, more preferably 550 to 950 ° C. The heat treatment time is appropriately adjusted so that the crystallization of the precursor glass proceeds sufficiently. Specifically, it is preferably 10 to 60 minutes, and more preferably 20 to 40 minutes.

  The positive electrode material for a lithium secondary battery of the present invention contains a conductive active material having a high electron conductivity and a stability in order to improve the conductivity with respect to the crystallized glass powder. The conductive active material is preferably supported on the crystallized glass powder interface. Examples of the conductive active material include carbon-based conductive active materials such as graphite, acetylene black, and amorphous carbon, and metal-based conductive active materials such as metal powder. As the amorphous carbon, those in which a C—O bond peak or a C—H bond peak causing a decrease in conductivity of the positive electrode material is not substantially detected in the FTIR analysis are preferable.

  The smaller the particle diameter of the conductive active material, the more uniformly it can be dispersed at each crystallized glass powder particle interface. Specifically, the particle diameter of the conductive active material is preferably 50 μm or less, and more preferably 30 μm or less. When the particle diameter of the conductive active material is larger than 50 μm, it tends to be difficult to uniformly disperse at each crystallized glass powder particle interface. Although it does not specifically limit about a minimum, It is 0.05 micrometer or more actually.

  As content of an electroconductive active material, it is preferable that it is 0.1-50 mass parts with respect to 100 mass parts of crystallized glass powder, It is preferable that it is 2-40 mass parts, 3-30 mass parts More preferably it is. If the content of the conductive active material is less than 0.1 parts by mass, the effect of imparting conductivity to the crystallized glass tends not to be sufficiently obtained. When the content of the conductive active material exceeds 50 parts by mass, the potential difference between the positive electrode and the negative electrode in the lithium ion secondary battery becomes small, and a desired electromotive force may not be obtained.

  As a method for supporting the conductive active material on the crystallized glass powder interface, glucose; a carboxylic acid such as an aliphatic carboxylic acid or an aromatic carboxylic acid; and an organic compound such as an organic binder are added to and mixed with the precursor glass powder. Heat treatment in an inert atmosphere such as nitrogen or a reducing atmosphere such as hydrogen, ammonia or carbon monoxide to crystallize the precursor glass powder, and amorphous carbon which is a conductive active material at the obtained crystallized glass powder interface The method of leaving the carbon component of this is mentioned. As described above, as the amorphous carbon, the CO bond peak or CH bond peak that causes the decrease in the conductivity of the positive electrode material is not substantially detected in the FTIR analysis by sufficiently performing the heat treatment. Is preferred.

  Here, examples of the aliphatic carboxylic acid include acetic acid, propionic acid, butyric acid, and oxalic acid. Examples of the aromatic carboxylic acid include benzoic acid, phthalic acid, maleic acid and the like. Examples of the organic binder include acrylic resin, polyethylene glycol, polyethylene carbonate, polymethylstyrene, and ethyl cellulose. Examples of the acrylic resin include polybutyl methacrylate, polyethyl methacrylate, and polymethyl methacrylate.

  According to the method, the conductive active material can be uniformly supported on the crystallized glass powder interface. In addition, the organic binder can contribute to two characteristics of the positive electrode material, that is, moldability and conductivity. That is, it can be easily formed into a sheet shape and can be used as a positive electrode material for a battery without being pulverized again after firing. Here, the temperature history of the heat treatment is as described for the crystallization process of the precursor glass. Specifically, it is appropriate to perform the heat treatment at least at the glass transition temperature or even at the crystallization temperature or higher. The upper limit is 1000 ° C, and further 950 ° C. If the heat treatment temperature is lower than the glass transition temperature, there is a possibility that a sufficient conductivity improvement effect cannot be obtained. On the other hand, if the heat treatment temperature exceeds 1000 ° C., the crystals may melt. The specific temperature range for the heat treatment is preferably 500 to 1000 ° C, more preferably 550 to 950 ° C. The heat treatment time is adjusted as appropriate so that the crystallization of the precursor glass can proceed sufficiently and the conductive active material can sufficiently remain at each crystallized glass interface. Specifically, it is preferably 10 to 60 minutes, and more preferably 20 to 40 minutes.

  In addition, there is a method in which a conductive active material is added to the crystallized glass powder and mixed. As addition amount of an electroconductive active material, it is preferable that it is 0.1-50 mass parts with respect to 100 mass parts of crystallized glass powder, It is preferable that it is 1-30 mass parts, 5-20 mass parts More preferably it is. When the addition amount of the conductive active material is less than 0.1 parts by mass, there is a tendency that the effect of imparting conductivity to the crystallized glass cannot be obtained sufficiently. When the addition amount of the conductive active material exceeds 50 parts by mass, the potential difference between the positive electrode and the negative electrode is reduced in the lithium ion secondary battery, and a desired electromotive force may not be obtained. In addition, when using an organic compound as an electroconductive active material, it is preferable to satisfy | fill content of the said range in graphite conversion.

The electrical conductivity of the positive electrode material for a lithium ion secondary battery of the present invention is 1.0 × 10 ⁻⁸ S · cm ⁻¹ or more and 1.0 × 10 ⁻⁶ S · cm ⁻¹ or more. Preferably, it is 1.0 × 10 ⁻⁴ S · cm ⁻¹ or more.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to this Example.

(Example 1: Preparation of precursor glass for positive electrode material of lithium ion secondary battery)
Samples were prepared using Li ₂ CO ₃ , Fe (II) C ₂ O ₄ .2H ₂ O, Nb ₂ O ₅ , NH ₄ H ₂ PO ₄ , and MnO ₂ as raw materials and having the molar ratios shown in Tables 1 to 3. A to C and J to U raw material powders were prepared and calcined at 300 ° C. for 10 hours in a nitrogen atmosphere to remove ammonia, water, etc., and then at 1200 ° C. for 15 minutes in a carbon monoxide atmosphere Melting was performed. Then, the glass sample was produced by press-cooling rapidly.

(Example 2: Production of crystallized glass powder for positive electrode material of lithium ion secondary battery)
Samples A to C and glass powders of J to U were uniaxially pressed to form a pellet with a diameter of 13 mmφ and a thickness of 1 mm, and then heat treated in a nitrogen atmosphere at the crystallization temperature obtained by differential thermal analysis for 5 hours. Went. The X-ray diffraction patterns after heat treatment for Samples A to C are shown in FIG. Regardless of the amount of Nb ₂ O ₅ added, LiFePO ₄ -derived diffraction lines were confirmed. In addition, it was confirmed that LiFePO ₄ crystals were also precipitated for samples J to P. Further, for samples Q～U, it was confirmed that crystal represented by Table 3 in LiMn _x Fe _1-x PO 4 as shown (0 <x <1) is precipitated. When gold electrodes were formed at both ends of the pellet and the electrical conductivity was measured by the alternating current impedance method, the precursor glass powder before crystallization was 10 ⁻¹¹ S · cm ⁻¹ , whereas crystallization after crystallization was performed. The glass powder exhibited an electrical conductivity of about 10 ⁻⁹ S · cm ⁻¹ . The glass transition temperature Tg and the crystallization temperature Tc were measured by differential thermal analysis.

(Example 3: Production of positive electrode material for lithium secondary battery 1)
The amount of graphite powder shown in Table 4 was added to the glass powder of Sample C to obtain a mixed powder. Thereafter, the mixed powder was formed into pellets so as to have a diameter of 13 mmφ and a thickness of 1 mm by uniaxial pressure molding to obtain samples D to I. Among the obtained samples, the powder X-ray diffraction patterns of Samples C, D, and G to I are shown in FIG. A diffraction line derived from graphite was confirmed in addition to the diffraction line derived from LiFePO _{4, and} it was found that graphite remained even after the heat treatment. Moreover, LiFePO ₄ crystallite size was determined using respective equations from the powder X-ray diffraction pattern Scherrer sample is estimated to be 20 to 60 nm.

  Gold electrodes were formed on samples D to I, and the electrical conductivity was measured in the temperature range of room temperature to 200 ° C. by the alternating current impedance method. FIG. 3 shows the temperature dependence of electrical conductivity. Table 4 shows the electrical conductivity at room temperature. As the amount of graphite increased, the electrical conductivity increased significantly. This indicates that the addition of graphite is effective in improving the electrical conductivity.

(Example 4: Production 2 of positive electrode material for lithium secondary battery)
After mixing 10 parts by weight of glucose (C ₆ H ₁₂ O ₆ ) powder (corresponding to 5.6 parts by weight in terms of graphite) with 100 parts by weight of the glass powder of Sample C produced in Example 1, uniaxial pressurization Molded into a pellet having a diameter of 13 mmφ and a thickness of 1 mm, and heat-treated in nitrogen at 800 ° C. for 30 minutes. The X-ray diffraction pattern after the heat treatment is shown in FIG. FIG. 4 also shows an X-ray diffraction pattern of only the glass powder of Sample C that was heat-treated. The presence of amorphous carbon was confirmed by measuring the Raman scattering spectrum.

Thereafter, gold electrodes were formed on both end faces of the sample, and the electrical conductivity was measured at room temperature by the alternating current impedance method. As a result, it was 1.76 × 10 ⁻³ S · cm ⁻¹ . From this, it can be considered that the amorphous carbon is coated on the grain boundary of LiFePO ₄ , which is more effective in improving the electrical conductivity than the sample mixed with graphite.

(Example 5: Production of lithium secondary battery positive electrode material 3)
30 parts by mass of powdered acrylic resin (polyacrylonitrile) (corresponding to 18.9 parts by mass in terms of graphite) and 3 parts by mass of butyl as a plasticizer with respect to 100 parts by mass of the glass powder of sample C produced in Example 1 The mixture was slurried by mixing benzyl phthalate and 35 parts by mass of methyl ethyl ketone as a solvent, formed into a sheet having a thickness of 200 μm by a known doctor blade method, and then dried at room temperature for about 2 hours. Next, this sheet material was cut into a predetermined size and heat-treated at 800 ° C. for 30 minutes in nitrogen.

Thereafter, gold electrodes were formed on both end faces of the sample, and the electrical conductivity was measured at room temperature by an alternating current impedance method. As a result, 1.4 × 10 ⁻³ S · cm ⁻¹ was shown. Moreover, when carbon content of the obtained sample powder was measured by EDX analysis, it was 5.3-6.2 mass% (5.6-6.6 mass with respect to 100 mass parts of glass powders) in arbitrary three places. It was confirmed that carbon was uniformly distributed. From this, it can be considered that the amorphous carbon is coated on the grain boundary of LiFePO ₄ , which is more effective in improving the electrical conductivity than the sample mixed with graphite.

  The positive electrode material for a lithium ion secondary battery of the present invention is suitable for portable electronic devices such as notebook computers and mobile phones, and electric vehicles.

It is a diagram showing the angle of the X-ray powder diffraction pattern and representative LiFePO ₄ diffraction lines of the crystals of the crystallized glass prepared in Example 2 (Sample A through C). Is a diagram showing the angle of the diffraction lines of the powder X-ray diffraction pattern and representative LiFePO ₄ crystal crystallized glass produced in Example 3 (Sample C, D, G~I). It is a figure which shows the temperature dependence of the electrical conductivity of the precursor glass (sample C) produced in Example 1 and 3, and the crystallized glass (sample CI). It is a diagram showing the angle of the diffraction line of X-ray diffraction pattern and representative LiFePO ₄ crystal powder sample prepared in Example 4.

Claims (14)

In mol% in terms of _{oxide, Li 2 O 20~50%, Fe} 2 O 3 5~40%, P 2 O 5 20~50% of the crystal for ruri lithium ion secondary battery positive electrode material to contain a composition A lithium ion secondary battery positive electrode material comprising a vitrified glass powder and a conductive active material . Claim wherein the crystallized glass powder further contains a MnO _2, the content of MnO ₂ of the crystallized glass powder is represented by mol% of oxide basis, of equal to or less than 55% 2. The lithium ion secondary battery positive electrode material according to 1 . The crystallized glass powder is further expressed in terms of mol% in terms of the following oxides: Nb ₂ O ₅ + V ₂ O ₅ + SiO ₂ + B ₂ O ₃ + GeO ₂ + Al ₂ O ₃ + Ga ₂ O ₃ + Sb ₂ O ₃ + Bi ₂ O _3. The lithium ion secondary battery positive electrode material according to claim 1 or 2 , characterized by containing a composition of 0.1 to 25%. The crystallized glass powder, according to any one of claims 1 to 3, characterized in that formed by precipitated LiFePO ₄ crystal or _{Li 3 Fe 2 (PO 4)} 3 crystals, or a solid solution thereof Lithium ion secondary battery positive electrode material . Said crystallized glass powder is made of by precipitating LiMn _X Fe _1-x PO ₄ crystal or _{Li 3 (Mn x Fe 1-} x) 2 (PO 4) 3 crystal (0 <x <1) The lithium ion secondary battery positive electrode material according to claim 4 . The lithium ion secondary battery positive electrode according to any one of claims 1 to 5, wherein the content of the conductive active material is 0.1 to 50 parts by mass with respect to 100 parts by mass of the crystallized glass powder. material. The lithium ion secondary battery positive electrode material according to claim 1, wherein the conductive active material is a carbon-based conductive active material. The lithium ion secondary battery positive electrode material according to claim 7 , wherein the carbon-based conductive active material is graphite, acetylene black, or amorphous carbon. (1) in mole% in terms of _{oxide, Li 2 O 20~50%, Fe} 2 O 3 5~40%, the step of preparing the batch to contain the composition of _P 2 O 5 20 to 50% (2) Step of melting the batch to obtain molten glass , ( 3) Step of rapidly cooling the molten glass to obtain precursor glass , (4) Step of pulverizing the obtained precursor glass to obtain precursor glass powder And (5) calcining the precursor glass powder at a glass transition temperature to 1000 ° C. to obtain a crystallized glass powder. In step (5), an organic compound is added to the glass powder to bring it into an inert or reducing atmosphere. A method for producing a positive electrode material for a lithium ion secondary battery, comprising activating a carbon-based conductive active material derived from an organic compound to crystallized glass powder by firing . In the step (1), when the batch is prepared, the batch further contains MnO _2, and the content of MnO _{2 in} the batch is 55% or less in terms of mol% in terms of oxide. The method for producing a positive electrode material for a lithium ion secondary battery according to claim 9 , wherein the batch is prepared so that: In the step (1), Nb ₂ O ₅ + V ₂ O ₅ + SiO ₂ + B ₂ O ₃ + GeO ₂ + Al ₂ O ₃ + Ga ₂ O ₃ + Sb ₂ O ₃ + Bi ₂ O _{3 in} terms of mol% in terms of the following oxides. The method for producing a positive electrode material for a lithium ion secondary battery according to claim 9 or 10 , wherein the batch is prepared so as to contain a composition of 0.1 to 25%. The method for producing a lithium ion secondary battery positive electrode material according to any one of claims 9 to 11, wherein the carbon-based conductive active material is amorphous carbon. The method for producing a positive electrode material for a lithium ion secondary battery according to any one of claims 9 to 12, wherein the organic compound is glucose, carboxylic acid, or an organic binder. The method for producing a positive electrode material for a lithium ion secondary battery according to claim 13 , wherein the organic binder is an acrylic resin.

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